I don’t have kids that age but I’m a qualified preschool educator. Get your child to socialise more.. Attachment in kids is common. They have separation anxiety when they are away from familiar adults. Bring your child out & about often. At home, get him/her to sit for solitary play, scribbling, colouring activities but monitor from far. It’s hard at first but it will get better.. Tell your child, you need to get something for a while, go toilet, get a drink, etc. Do not lie. Otherwise, you’ll break his/her trust. When you come back to join your child, thank him/her for waiting! Hope this helps! Keep me posted!!